RE: [PATCH v2 3/3] Make core_pattern support namespace

[Zhao Lei <zhaolei@cn.fujitsu.com>]

Hi, Eric

> -----Original Message-----
> From: Eric W. Biederman [mailto:ebiederm@xmission.com]
> Sent: Tuesday, March 22, 2016 5:25 AM
> To: Zhao Lei <zhaolei@cn.fujitsu.com>
> Cc: linux-kernel@vger.kernel.org; containers@lists.linux-foundation.org;
> 'Mateusz Guzik' <mguzik@redhat.com>; 'Kamezawa Hiroyuki'
> <kamezawa.hiroyu@jp.fujitsu.com>
> Subject: Re: [PATCH v2 3/3] Make core_pattern support namespace
> 
> Zhao Lei <zhaolei@cn.fujitsu.com> writes:
> 
> > Hi, Eric
> >
> >> -----Original Message-----
> >> From: Eric W. Biederman [mailto:ebiederm@xmission.com]
> 
> > Let me make a summarize:
> > You think this way is not acceptable, because the pipe program is running
> > in the panic-process's namespace context.
> 
> Actually my view is that your patchset is not acceptable because it
> is implemented in a way that is not backwards compatible (AKA it can
> break existing configurations that remain unchanged) and your
> implementation does not appear in the least safe from malicious users.
> 
> There is also a problem that your patchset is simply buggy for what it
> tries to implement, as using pid_ns_for_children and the multiple kbuild
> robot emails testifies.
> 
> > And in my view, a pipe program in the host's top level namespace is also
> > a problem.
> >
> > Let us think a container, to make it act as a real machine, when a program
> > panic, linux kernel should dump it into the container's filesystem.
> >
> > For the kernel, to keep the current way of forking pipe program by kthread,
> > just let the pipe thread running in the container's namespace, instead the
> host,
> > may solve the problem in current kernel.
> >
> > What is your opinion?
> >
> > Btw, this patch is trying to solve the problem descripted in thread named:
> > "piping core dump to a program escapes container" in
> >
> http://lists.linuxfoundation.org/pipermail/containers/2015-December/036476.
> html
> > Maybe using a userspace tool can make container dump to anywhere,
> > but for kernel ifself, it is better to solve above problem if we can.
> 
> I think it would be great to find a way to run a core dump helper and
> otherwise allow setting the core dump pattern in a container in a way
> that is safe from malicious users and does not break existing setups.
> 
So, there is following problem:
1: safe from malicious users
  We can try to find a way to fork process which have no relationship
  with the panic process.
2: Bug in patch
  It can be fixed, but I'd rather get a conclusion of this discussion
  before fix.
3: Backwards compatible
  It maybe the biggest problem in discussion, this patch is used to let
  container dump files into container, it is different with current action.
  Before patch:
    File type dump_pattern: dump to container
    Pipe type dump_pattern: dump to host
  After patch:
    File type dump_pattern: dump to container
    Pipe type dump_pattern: dump to container
  The second design seems better but not compatible with current kernel,
  but this patch can not fix to keep compatible because it is the patch's
  function.
  Maybe we can make some workagound, as:
  a. Add a kernel config to let the old style as default.
  b. keep old style, and add "||" for core_pattern, as
    echo "|| /root/container_dumper" >/proc/sys/kernel/core_pattern
    to dump to container.

  What is your opinion about it?

Thanks
Zhaolei